Multicast or broadcast is a technology of data transmission from a single data source to multiple destinations. In the traditional mobile networks, Cell Broadcast Service (CBS) permits the data of low bit-rate to be transferred to all the users via a shared broadcast channel of the cell. The CBS service is a type of message services.
At present, telephone and message services are not enough to satisfy people's demands of mobile communication. With the rapid development of the Internet, many kinds of multimedia services come forth, wherein some application services require multiple users to receive the same data at the same time, such as Video-On-Demand (VOD), telecast, video conference, network-based education and interactive video games. Compared with common data services, the mobile multimedia services have such features as large data capacity, long duration and high sensitivity to time delay. The mobile networks have specific network structure, function entities and wireless interfaces, which are very different from the cable IP networks. Therefore, the existing IP multicast technologies are only applicable to the cable IP networks, but not to the mobile networks.
To utilize resources of the mobile networks effectively, WCDMA/GSM International Organization for Standardization (ISO) 3GPP has put forward a concept of Multimedia Broadcast/Multicast Service (MBMS) service to provide point-to-multipoint services of transmitting data from one data source to multiple users, which realizes shared utilization of network resources, improves the efficiency thereof, especially the utilization efficiency of the air interface resource. The MBMS defined by the 3GPP can not only realize the multicast/broadcast of plain text and low data-rate message, but also support high-speed multimedia multicast/broadcast services, which undoubtedly conforms to the development trend of the future mobile communication.
FIG. 1 illustrates a wireless network architecture that supports multicast/broadcast services. As shown in FIG. 1, in the existing specifications of 3GPP, a wireless network entity that supports multicast/broadcast services is a Broadcast/Multicast Service Center (BM-SC) 101. The BM-SC 101 is connected with a Gateway GPRS Support Node (GGSN) 102 through a Gmb interface or a Gi interface, and one BM-SC 101 can be connected with multiple GGSNs 102. The GGSN 102 is connected with a Serving GPRS Support Node (SGSN) 103 through a Gn/Gp interface, and one GGSN 102 can be connected with multiple SGSNs 103. The SGSN 103 is connected with a UMTS Terrestrial Radio Access Network (UTRAN) 104 through an Iu interface, and the UTRAN 104 is connected with a UE 106 through a Uu interface. The SGSN 103 may also be connected with a GSM Enhanced Radio Access Network (GERAN) 105 through an Iu/Gb interface, and the GERAN 105 is connected with a UE 107 through a Um interface.
The network architecture in FIG. 1 shows that, to support the MBMS service, a mobile network function—Broadcast/Multicast Service Center, i.e. a BM-SC, is added in the 3G Mobile Communication System. The BM-SC is an entrance for an Internet Content Provider (ICP), which is used for authorization and to initiate MBMS bearer services on the mobile networks as well as to schedule and deliver the MBMS transmissions. In addition, functions related to MBMS are added to such functional entities as UE, UTRAN, GERAN, SGSN and GGSN.
MBMS includes a multicast mode and a broadcast mode, wherein the multicast mode needs users to subscribe to a corresponding multicast group, activate services and generate relevant billing information. Different service demands of multicast mode and broadcast mode result in different procedures of respective services. FIG. 2 is a flowchart of the MBMS multicast mode and FIG. 3 is a flowchart of the MBMS broadcast mode.
As shown in FIG. 2, the processes related to the MBMS multicast service comprises: Subscription, Service announcement, Joining, Session Start, MBMS notification, Data transfer, Session Stop and Leaving. The Subscription process is used to make users subscribe to services which the users needed in advance. The Service announcement process is a process of the BM-SC announcing the services that can be provided currently. The Joining process is an activation of the MBMS multicast service, through which the UE informs the network that the UE wants to be a member of a current multicast group voluntarily and to receive multicast data of the corresponding services. In the Joining process, MBMS UE context that records the UE information is created on both the network and the UE joining the multicast group. In the process of Session Start, the BM-SC gets ready to transfer data and instructs the network to establish bearer resources of the corresponding core network and access network. MBMS notification process is used to inform UE that an MBMS multicast session is about to start. In the process of Data transfer, the BM-SC transfers the data to the UE through the bearer resources established in the Session Start process.
The MBMS service has two modes for transmission between the UTRAN and the UE: a point-to-multipoint (PTM) mode and a point-to-point (PTP) mode. In the PTM mode, same data are transferred through an MBMS point-to-multipoint Traffic Channel (MTCH), and all the UE joining in multicast services or interested in broadcast services can receive the data. In the PTP mode, data are transferred through a Dedicated Channel (DTCH), and only the relevant UE can receive the data. The Session Stop process is used to release the bearer resources established in the process of the Session Start. The Leaving process makes the subscribers of a group leave this multicast group, which means the users will not receive the multicast data any more. In the Leaving process, the relevant MBMS UE context is deleted.
As shown in FIG. 3, processes related to the MBMS broadcast service are similar to those of the MBMS multicast service. However, in the MBMS broadcast service, the Subscription and Joining processes are not needed before the Session Start process, and the Leaving process is not needed after the Session Stop process.
As shown in FIG. 2, in the MBMS multicast service, the processes of Joining and Session Start are independent from each other, i.e. a user may join a multicast service before a session is started or at any time during the session after the session is started.
Generally, after the Session Start process of a certain MBMS service, the RNC will adopt an appropriate bearer mode, a PIP mode or a PTM mode, according to the number of the users receiving the MBMS service in one cell. For the PTP mode, a user DCH that receives the service, such as a Dedicated Physical Channel (DPCH), is used as the bearer of the MBMS traffic; while for the PTM mode, a common channel (FACH), such as a Secondary Common Control Physical Channel (SCCPCH) is used as the bearer of the MBMS traffic. The number of the users receiving the MBMS service in a cell is obtained by a Counting process.
In existing protocols, the procedures of the CN and UTRAN processing a certain MBMS service specifically comprise:
1) In a Joining process, a user instructs the network to get ready to receive the MBMS service;
2) In an MBMS Session Start process, the CN notifies the UTRAN that a certain MBMS service session is about to start, wherein the Session Start notification contains an ID and a property of the MBMS service;
3) Having received the Session Start notification, the UTRAN initiates Counting processes in the cells that the MBMS service is requested to select a proper bearer mode of the MBMS service for the cells;
4) During the MBMS service session, processes of recounting users are carried out to verify whether the selected bearer mode is proper or not.
However, there are some disadvantages in the prior art. According to the solution in the prior art, in order to select a bearer mode for an MBMS service, a Counting or Recounting process is likely to be performed at the beginning of the session or during the session of the MBMS service. Such a process of selecting the proper bearer mode by counting or recounting is very complicated and time consuming. For example, in the counting process, it has to be taken into account whether users of different states currently demand the MBMS service or not. For users in idle state but having the demand for the MBMS service, an RRC (Radio Resource Control) connection should be established; the idle-state users have to perform the probability detection, and initiate the random access process in the Random Access Channel (RACH) if passing the detection. As a result, there will be a heavy load of signaling in the air interface, and blocks are likely to come forth in the upstream direction. For users in the URA-PCH (UTRAN Registration Area Paging Channel) state, on the other hand, a cell updating process is needed. Moreover, after a Counting process stops, according to the algorithm of Radio Resource Management (RRM), some or all users are likely to return to the idle state or x-PCH state, such as CELL-PCH state or URA-PCH state.
In addition, counting errors during the Counting process may result in the establishment of improper bearer mode, which means the Counting process has not played the proper role. Moreover, to accomplish counting, the power consumption at the UE will be increased during the random access process and the cell updating process performed by the idle-state users or URA-PCH-state users.
It can be seen from the above description that the system has to perform the Counting process at a relatively great cost.